Our goal in this project is to establish biological understanding, preclinical proof of concept; and safety data using AAV-based vectors for correction of familial hypercholesterolemia (FH) and abetalipoproteinemia (ABL) such that clinical trials of gene therapy for both disorders is a tangible reality by the final year of this P01. Dyslipidemia is a major risk factor for atherosclerotic cardiovascular disease (ASCVD), the most common cause of death and disability. Several common genetic forms of dyslipidemia exist and although many patients with dyslipidemia can be treated effectively with existing drugs, others are not effectively treated and remain at exceptionally high risk of premature ASCVD. A classic example is homozygous FH, in which patients have severe hypercholesterolemia that can't be effectively treated with current drugs and develop ASCVD in childhood or adolescence. Conversely, ABL, which is due to mutations in the microsomal triglyceride transfer protein (MTP), is associated with absent plasma LDL and apoB and progressive spinocerebellar degeneration and retinopathy. Therefore, understanding of the regulation of the secretion and catabolism of apoB-containing lipoproteins by the liver is of major importance to the development of new therapies targeted toward these pathways. Liver-directed somatic gene transfer is a useful biological tool that could be used as a strategy for treating severe dyslipidemia. In this project, we will utilize liver-directed gene transfer using vectors based on novel adeno-associated virus (AAV) pseudotypes to address questions related to the impact of specific gene products on the regulation of hepatic secretion of apoBcontaining lipoproteins. Project I will identify the best AAV for liver-directed gene transfer (called AAVcc) which will be further evaluated in this project. Specific Aim 1 will use mouse models of FH to test the hypothesis that AAVcc-mediated expression of the murine LDL receptor (LDLR) will stably normalize cholesterol levels and prevent, and regress, atherosclerosis. Specific Aim 2 will test the hypothesis that AAV8-mediated expression of the rabbit LDL receptor (LDLR) will stably normalize cholesterol levels and prevent, and regress, atherosclerosis in LDLR-deficient WHHL rabbits. Specific Aim 3 will test the hypothesis that AAVcc-mediated expression of the rhesus LDL receptor (LDLR) wilj stably normalize cholesterol levels in the heterozygous LDLR-deficient rhesus fed a high-fat high-cholesterol diet designed to downregulate the expression of the LDLR from the normal allele. Specific Aim 4 will test the hypothesis that AAVcc-mediated expression of the murine MTP will stably permit secretion of apoB-containing lipoproteins by the liver in the liver-deficient MTP mouse. Effects on vitamin E metabolism and end-organ effects will also be determined.